In the aeronautical field, onboard equipment called TAWS systems (Terrain Awareness and Warning Systems) have been developed to warn of the risks of collision with the ground. These TAWS systems provide a short or medium term prediction of the path of the carrier aircraft, based on flight information (position, heading, orientation and amplitude of the speed vector) supplied by the onboard instruments, placing it in a situation relative to a map of the region being flown over extracted from a database of elevations of the terrain and flight prohibition zones, accessible on board and issuing alarms to the crew of the aircraft each time the short or medium term predictable path comes into collision with the ground. Some TAWS systems add to their alarms rudimentary recommendations of the “Terrain Ahead, Pull up” type. Others also give information on the levels of the risks of collision provided by the reliefs, the obstacles and the flight zones prohibited by regulations present in the maneuvering zone of the aircraft, in the form of a map showing the area of the globe being flown over divided into layers of different colors according to the scale of the risk involved.
There is an interest in going further in navigation assistance and signaling to the crew of a moving vehicle, its margin of maneuverability at the boundaries of the zones considered uncrossable.
In the field, the applicant has proposed, in a French patent application FR 2.842.594 filed on 19 Jul. 2002, a system for preventing the risks of collision with the ground for an aircraft, likening the risks of collision with the ground to the penetration of the relief of the zone being flown over into the protection envelope linked to the aircraft, and quantifying them according to the time remaining to undertake an avoidance maneuver. The protection envelopes linked to the aircraft are defined in the horizontal plane, by the surfaces swept by rings with radii greater than that of a predefined avoidance turn, placed, to right and left of the aircraft and offset in front of the aircraft, on its path that can be predicted in the short or medium term. The ground collision risk prevention system quantifies the risks according to the time remaining to the aircraft to undertake, with respect to a relief considered to be threatening, a lateral avoidance maneuver having a point of no-return where the clearance paths by means of a turn corresponding to the pre-established avoidance turn are no longer effective.
The applicant has also proposed, in a French patent application filed on 19 Dec. 2003 under the number 0315020, displaying in the cockpit of an aircraft, a maneuverability map representing the terrain zone being flown over as three types of region: a first type corresponding to the regions to be bypassed as they are considered uncrossable because of the situation and the present performance characteristics of the aircraft, for example, by a TAWS system or even being the subject of a regulatory flight prohibition, a second type corresponding to zones with restricted lateral maneuvering freedom, consisting of the lateral fringes surrounding the regions to be bypassed, of a width corresponding to a minimum width estimated to be necessary to the aircraft to describe, flat and at a safe height, a waiting pattern, and a third type of region complementing the other two types, corresponding to areas with lateral maneuvering freedom. This navigation map, created from a database of elevations of the terrain and of prohibited zones, applies a propagation distance transform for the placement of the external contours of the zones with restricted lateral maneuvering freedom.
The applicant has also proposed, in a French patent application filed on 18 Jun. 2004 under the number 04 06654, a system for signaling narrow passages of the path of a flight plan where the lateral maneuvering freedom of the aircraft is restricted laterally by reliefs or zones that are subject to a regulatory flight prohibition. This signaling system detects the risks of collision with the ground according to the method normally employed by the TAWS systems, which consists in likening the risks of collision with the ground to the penetration of the relief or prohibited zones into protection envelopes linked to the aircraft. In the case of this signaling system, the protection envelopes linked to the aircraft delimit a space considered insufficient to allow the aircraft to perform flat turns that are as tight as is allowed, taking into account the wind.